1. Field of the Invention
The present invention relates generally to the field of molecular biology and stem cells. More particularly, it concerns reprogramming of somatic cells, especially hematopoietic progenitor cells.
2. Description of Related Art
In general, stem cells are undifferentiated cells which can give rise to a succession of mature functional cells. For example, a hematopoietic stem cell may give rise to any of the different types of terminally differentiated blood cells. Embryonic stem (ES) cells are derived from the embryo and are pluripotent, thus possessing the capability of developing into any organ or tissue type or, at least potentially, into a complete embryo.
Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell. Induced pluripotent stem cells are believed to be identical to natural pluripotent stem cells, such as embryonic stem cells in many respects, such as in terms of the expression of certain stem cell genes and proteins, chromatin methylation patterns, doubling time, embryoid body formation, teratoma formation, viable chimera formation, and potency and differentiability, but the full extent of their relation to natural pluripotent stem cells is still being assessed.
IPS cells were first produced in 2006 (Takahashi et al., 2006) from mouse cells and in 2007 from human cells (Takahashi et al., 2007; Yu et al, 2007). This has been cited as an important advancement in stem cell research, as it may allow researchers to obtain pluripotent stem cells, which are important in research and potentially have therapeutic uses, without the controversial use of embryos.
In humans, iPS cells are commonly generated from dermal fibroblasts. However, the requirement for skin biopsies and the need to expand fibroblast cells for several passages in vitro make it a cumbersome source for generating patient-specific stem cells. Moreover, previous methods for reprogramming of human somatic cells are inconvenient because they need to obtain somatic cells directly from a human subject, or maintain the cells in a labor-intensive cell culture system.
Therefore, there is a need to develop methods to induce pluripotent stem cells from alternative sources which are simple, convenient, and easily accessible. In developing the present invention, the inventor considered that blood cells may be such a source because blood may be collected from a patient or a healthy individual, stored or transferred, for example, from a central unit for distribution to one or more remote places. However, there remains a need to develop more efficient methods for reprogramming blood cells, especially peripheral blood cells.